Fluidized catalytic cracking processes were developed during the 1940's to increase the amount of naphtha boiling range hydrocarbons which could be obtained from crude oil. Fluidized catalytic cracking processes are now in widespread commercial use in petroleum refineries to produce lighter boiling point hydrocarbons from heavier feedstocks such as atmospheric reduced crudes or vacuum gas oils. Those knowledgeable in the art are therefore believed capable of adequately designing and operating FCC processes. Evidence of this is provided by several competing commercial designs shown in the articles at page 102 of the May 15, 1972 edition and at page 65 of the Oct. 8, 1973 edition of the "Oil and Gas Journal".
In a fluidized catalytic cracking process, "spent" catalyst is removed from a reaction zone and transferred into a regeneration zone. Carbonaceous deposits on the catalyst are burned within the regeneration zone. This generates a significant amount of heat. Those skilled in the art are cognizant of the fact that depending on the operational mode of the regeneration zone and the charge stock being processed in the FCC unit it is necessary or desirable to remove heat from the regeneration zone. This is described in U.S. Pat. No. 2,926,143 to M. B. Leland and U.S. Pat. No. 4,430,302 to B. J. Krause. These two references describe heat exchange coils placed within the large catalyst regeneration vessel. U.S. Pat. No. 4,434,245 issued to D. A. Lomas et al and U.S. Pat. No. 4,438,071 issued to A. G. Vickers are pertinent for their showing of the use of heat exchangers mounted externally to the overall catalyst regeneration vessel. These references describe a flow-through type catalyst cooler and a backmix type external catalyst cooler.
Heat pipes are a mechanical apparatus known to those in the heat transfer arts. It is believed heat pipes were first described in U.S. Pat. No. 2,350,348 to R. S. Gaueler. Heat pipes are very efficient at transferring heat between two different locations. Heat pipes basically comprise an outer cylindrical conduit which is sealed to retain a small amount of working fluid which may be vaporized and condensed at the temperatures of the heat source and heat sink respectively. A porous wick is located within the heat pipe to transfer liquid from the cool end to the warm end of the heat pipe. Heat pipes are described in greater detail in the article beginning at page 30 of the February 1967 edition of "Mechanical Engineering" and in an article beginning at page 38 of the May 1968 edition of "Scientific American", Volume 128, No. 5.
The use of a heat pipe to remove heat from a reaction zone is described in U.S. Pat. No. 3,971,634 issued to W. A. Renken et al. This reference is also pertinent in that the heat removed from the reaction section, which is a methanation zone, is transferred to a heat exchange section suitable for transferring heat to a cooling fluid. British Pat. No. 1,599,398 issued to K. F. Shaw is pertinent for its suggestion that heat pipes can be employed in a fluidized catalytic cracking process. The teaching in this reference is believed to be limited to the transfer of heat from the regeneration zone to the reaction zone in an FCC unit. British patent application No. 2,126,119 issued to R. A. McAllister is pertinent for its teaching that heat pipes may be used to remove heat from a fluidized bed reactor and transfer this heat to a heat sink wherein the heat is removed as by radiation, forced air, convection, water cooling, or the like. These references do not appear to touch upon the heat removal control system described herein.